Analysis of cells, such as blood cells, may be accomplished by staining the cells with a fluorescent dye and then detecting a fluorescent emission as individual cells pass through a narrow illuminated flow chamber. U.S. Pat. Nos. 3,788,744 and 3,819,270 illustrate conventional techniques and U.S. Pat. No. 3,788,744 describes apparatus for such photoanalysis. This type of photoanalysis is usually performed on several million particles in any particular sample. Since it is always desirable for the complete sample to be measured in only a few minutes, the measurement time allowed for a single particle is in the order of microseconds. As a result, the total integrated signal output from a photodetector responsive to the fluorescent emissions of individual cells is quite weak. If a more substantial signal is required in order to discriminate between different classes of particles, it is necessary to increase the measurement time by reducing the flow rate of particles through the flow chamber. Alternatively, the length of the measurement chamber may be increased and the particle concentration diluted to prevent the possibility that two particles will be in the measurement area of the flow chamber simultaneously. In either case, the total time for analysis of the entire sample is increased. The same problem exists whether the cell counter used is designed for photometric analysis, or whether it operates on a principle of detecting differences other than fluorescent emission. For example, commercial blood cell counters are available which operate on the principle of distinguishing between cells on the basis of electrical conductivity, light scattering, light blockage, or electrical capacitance. U.S. Pat. No. 3,811,841 describes a system employing light blockage in cell detection.